The fight for catalytic converters has moved to America's backyards – literally. The EPA and state regulators in California, are calling for mandatory converters in lawnmowers to cut down on their surprisingly high amount of emissions (according to the New York Times, putting catalytic converters on lawnmowers in California would be the equivalent of taking over 800,000 cars—daily!—off the road—a testament to how clean cars have become). Engine makers, on the other hand, argue that these converters will create a fire hazard in owner's sheds, similar to the debates that raged in the '70s about fire hazards from automotive cat converters.

The problem isn't limited to lawnmowers—just about all 2-stroke engines without a converter (such as most portable generators) can also produce disproportionately high emissions—a health risk that's starting to get addressed by engine manufacturers.

In March, the EPA gave a green light to catalytic converters on lawnmowers and small engines, saying they were safe and would improve the air. (Catalytic converters reduce smog-forming nitric oxide and nitric dioxide, and other toxic byproducts of engines.)

U.S. Senator Dianne Feinstein, a lawnmower cat converter advocate, said that studies have shown that cutting grass with a gas powered lawnmower causes as much pollution as operating a car for 13 hours.